A parking brake system for a vehicle is designed to prevent movement of a parked vehicle. A traditional parking brake system is manually operated. The driver needs to physically pull a lever to apply the parking brake. Electric parking brake (EPB) systems replace the traditional parking brake system. The EPB system includes a number of actuators, each having an electric motor, to operate the brakes of the vehicle. The actuator may include a lead screw or a ball screw. The user presses a button to operate the motor to rotate the lead screw or the ball screw of the actuator, thereby applying the brakes.
However, the actuator using the lead screw has a low efficiency. Although the use of the ball screw can improve the efficiency for the actuator, the actuator cannot self-lock. If the vehicle is positioned on a slope, the vehicle may start moving after applying the brakes as the actuator ‘relaxes’. Alternatively, the motor needs to remain active the entire time the parking brake is active, which is not a desirable situation due to the obvious safety issues.